ASTM D5188 Standard Test Method for Vapor-Liquid Ratio Temperature Determination of Fuels (Evacuated Chamber and Piston Based Method)
4. Summary of Test Method
4.1 A known volume of chilled, air-saturated sample is introduced into an evacuated, thermostatically controlled test chamber of known volume or a test chamber with moveable piston that expands the volume after sample introduction, the internal volume of which is V/L+1 times of that of the total test specimen introduced into the chamber. The sample volume is calculated to give the desired vapor-liquid ratio for the chamber volume in use. After injection, the chamber temperature is adjusted until a stable chamber pressure of 101.3 kPa (14.69 psia) is achieved.
5. Significance and Use
5.1 The tendency of a fuel to vaporize in automotive engine fuel systems is indicated by the vapor-liquid ratio of the fuel.
5.2 Automotive fuel specifications generally include T(V/L = 20) limits to ensure products of suitable volatility performance. For high ambient temperatures, a fuel with a high value of T(V/L = 20) , indicating a fuel with a low tendency to vaporize, is generally specified; conversely for low ambient temperatures, a fuel with a low value of T(V/L = 20) is specified.
